Electrolytic cellstructure

ABSTRACT

THE ANODES OF DIAPHRAGM TYPE ELECTROLYTIC CELLS OF EITHER MONOPOLAR OR BIPOLAR DESIGN ARE SECURED TO SPACER BARS, WHICH ARE ATTACHED TO A BASE PLATE, WITH BOLTS RUNNING PARALLEL TO THE BASE PLATE THROUGH PRESSURE BARS ON BOTH SIDES OF THE ANODES. ONE PRESSURE BAR IS THREADED TO RECEIVE THE THREADS OF THE BOLT, WHILE THE OTHER PRESSURE BAR IS DRILLED AND COUNTERSUNK TO RECEIVE THE HEAD OF THE BOLT. THE BOLTED ANODE ASSEMBLY PROVIDES A LOW RESISTANCE JOINT WHICH PERMITS OPERATION OF AN ELECTROLYTIC CELL AT HIGHER CURRENT DENSITIES WITHOUT ENCOUNTERING EXCESSIVE VOLTAGES. FURTHERMORE, THE ANODES MAY BE SHORTER IN THE BOLTED ASSEMBLY BECAUSE LESS STUB LOSS IS INVOLVED THAN IN THE CONVENTIONAL CAST LEAD BASE COVERED WITH MASTIC.

' 115i.16,1971v 1 MRGRQTHEER I 3,563,878'

"ELECTROLYTIC: CELL STRUCTURE v I Filedfiul y s 19 68- I I I 5Sheets-Sheet 1 Feb. 16, 1971 M. P. GROTHEIER 3,563,878

ELECTROLYTIC CELL STRUCTURE mm Uu1y 5. 1968 I 5 sheeitsfiwfl 2 Feb l fi,1971 PQGROTHEER 3,

' ELECTROLYTIC CELL STRUCTURE I 5 Sheets-Sheet 3 Mg- P. GROTHEER3,563,878 ELECTROLYTIC CELL STRUCTURE Feb. 16, 1971- 5 Sheets-Sheet 4Filed July 5,. 1968 I I h 'n M. P. 6R0] em 3,510.3,3

ELECTROLYTIC: CELL STRUCTURE Feb, 16,1971

5 Shets-Sheet 5 Filed Jill 5, 1968 United States Patent Oflice 3,563,878Patented Feb. 16, 1971 3,563,878 ELECTROLYTIC CELLSTRUCTURE Morris P.Grotheer, Lewiston, N.Y., assiguor to Hooker Chemical Corporation,Niagara Falls, N.Y., a corporation of New York Filed July 5, 1968, Ser.No. 742,892 Int. Cl. C22d 1/02 US. Cl. 204256 9 Claims ABSTRACT OF THEDISCLOSURE The anodes of diaphragm type electrolytic cells of eithermonopolar or bipolar design are secured to spacer bars, which areattached to a base plate, with bolts running parallel to the base platethrough pressure bars on both sides of the anodes. One pressure bar isthreaded to receive the threads of the bolt, while the other pressurebar is drilled and countersunk to receive the head of the bolt. Thebolted anode assembly provides a low resistance joint which permitsoperation of an electrolytic cell at higher current densities withoutencountering excessive voltages. Furthermore, the anodes may be shorterin the bolted assembly because less stub loss is involved than in theconventional cast lead base covered with mastic.

BACKGROUND OF THE INVENTION The ever increasing demand for products ofelectrolytic cells has necessitated a continuous development of newelectrolytic cells which operate on higher current capacity and currentdensity in both diaphragm and mercury type cells. Diaphragm cells havetwo main advantages over mercury type cells. The advantages are low cellvoltages and low investment costs. Developments in diaphragm cellstrending toward higher current capacities and current densitiesadvantageously will also involve fewer cell parts and minimize the floorarea needed to house many units. Generally, electrolytic cells of thefingered bipolar cell design are consistent with the goals of theindustry.

Fingered bipolar type electrolytic cells are known. Likewise, inmonopolar diaphragm type electrolytic cell design, any improvementleading to operation at lower cell voltage, higher current density andgreater output per cell floor area is a decided advantage.

It is an object of this invention to provide a diaphragm type cell of ahigh current rating.

Furthermore, it is an object of this invention to provide an anodeassembly for use in monopolar and bipolar diaphragm type electrolyticcells which excells in ease of assembly.

And, it is an object of this invention to provide an anode assembly forelectrolytic cells which provides a smaller voltage drop between theanode and the current conductor than is obtainable from normalanode-lead base connections.

BRIEF DESCRIPTION OF THE INVENTION In accordance with this invention,there is provided an electrode assembly for an electrolytic cellcomprising a base plate having attached thereto plural electroconductivespacer bars to which the electrodes are clamped and held in position bytwo pressure bars and a bolt running parallel to said base plate throughholes in the electrode, spacer bar and pressure bar assembly.

Basically, this unitary electrode assembly involves a metallic(preferably steel) base plate or backer plate to which spacer bars of anelectrically conductive material such as platinized-titanium, aluminumalloys and preferably copper are attached by welding, tinning, boltingor by other mechanical means to the steel at predetermined intervalsbased upon the desired pitch of the anodes. When the spacer bar isconstructed from platinized titanium, the use of sealants may bedispensed with as protective means against attack by the corrosivematerials which contact it. The spacer bar is disposed in such a mannerthat the attached anodes will be aligned with abutting edges verticallysituated within the cell unit. The spacer bar contains holes throughwhich pass the bolts running parallel to the base plate. The holesthrough the spacer bars are preferably slotted, at an angle downwardlyextending from the vertical bar surface. The number of anodes that maybe attached to the spacer bars by pressure bars depends upon thedesigned height of the cell where the anodes are horizontally attachedto the spacer bar in a vertically disposed bank of anodes, or the cellwidth where the anodes are vertically attached to the spacer bar in abank extending across the cell.

The pressure bars, one being drilled and countersunk,

the other being provided with threaded holes, act, in conjunction withthe bolt running through them, the anode and spacer bar, as an electrodeclamping device. In the clamped position, the electrical resistancethrough the anode-spacer bar contact is a function of the pressuredeveloped at the contacting surfaces. Hence, the resistance developedthrough the clamped connection of anode and spacer bar may be controlledby regulating the pressure applied by the clamping bolts. Considerationmust also be given to the thermal expansion of the spacer bar duringoperation of the cell in which temperatures above C. are common. Inpractice, the bolts may be of a suitable metal or metal alloy tocompensate for the expansion of the spacer bars and pressure bars.

The pressure bars may be made of any suitable material, such as steel.The electrode assembly may be employed in diaphragm type electrolyticcells to produce a desired product such as chlorine, caustic andhydrogen or an alkali metal chlorate.

The electrodes are loosely assembled initially, two at a time, placed onthe permanent spacer bar with the bolts in the slotted holes. The boltsare tightened to firmly clamp the anodes to the spacer bar. After theanodes have been installed, a sealant is placed over the connectingmembers between each electrode.

Any corrosion resistant sealant known to the art may be employed. Forexample, natural or synthetic rubbers may be employed by themselves, incombination or in conjunction with other resins. Bituminous materialsmay be employed if desired and the phenol-formaldehyde resins andpolyester resins are acceptable sealants. Especially good sealants maybe derived from the reaction of a polyhydric alcohol with a Diels-Alderadduct of hexahalocyclopentadiene and an alpha, beta unsaturateddicarboxylic acid, such as are disclosed in US. 3,216,884. The sealantsemployed in this invention may be advantageously highly filled with suchmaterials as sand, SiO graphite particles or other inert materials.

The applicable electrodes in the present invention comprise graphite,metals, metal oxides and combinations thereof. The metallic electrodescomprise an electro-conductive substrate metal with an active surface.By substrate metal it is intended to encompass those metals and metalalloys which become passivated when polarized anodically and remainpassive well beyond the anodic potential needed to convert a chlorideion to chlorine.

The phenomenon of passivity in this connection is discussed in anarticle by Greene, appearing in the April 1962 issue ofCorrosion-National Association of Corrosion Engineers, pages 1361 to142t, wherein reference may be made to FIG. 1 which describes a typicalactive-passive transition of a metal toward a corrosive medium. Themetal substrate employed in the electrodes applicable in this inventionwill not pass into the transpassive range until a potential is reachedwhich is considerably higher than that needed to produce chlorine fromthe chloride ion. Hence, the substrate metal remains passive during theoperation of the electrolytic cell.

Illustrative of the substrate metals in a generic sense are the valvemetals (with the exclusion of certain metals which obviously areinapplicable such as aluminum, zirconium, and the like). Titanium,tantalum or niobium are acceptable substrate metals. The titaniumemployed is normally a commercially pure grade of titanium ofintermediate strength. Alloys of titanium may be employed as long as thealloy meets the criterion of passivity set forth in the precedingparagraph. For example, titanium alloys of aluminum, vanadium,palladium, chromium or tin may be employed in which the latter metalsare present as less than about 10 percent of the alloy.

The surface of the substrate metal may be made active by variousmethods. For example, a conductor such as a noble metal (preferablyplatinum) may be deposited on the surface of the substrate metal bymethods known to the art such as electrodeposition. Mixtures of noblemetals and platinum may be used to activate the surface of the metalsubstrate. The preferred surface metal mixture or alloy is onecontaining more than about 50 percent platinum. Likewise, noble metaloxides may be used alone or in combination with noble metals to form theactive electrode surface. By noble metal, it is intended to include theplatinum and palladium triads of the Periodic Table with the exclusionof osmium. Thus, ruthenium, rhodium, palladium, irridium and platinumrepresent noble metals which are especially applicable in their metallicform, alloys thereof and as oxides.

The electrode substrate metal upon which an active surface, as describedin the preceding paragraph, is applied need not be homogeneous in crosssection. For example, the substrate metal or alloy may be clad upon anelectrically conductive core. In this sense, the core may consist of anyelectrical conductor of which aluminum, steel and especially copper areexemplary. The substrate metal may be clad to the electricallyconductive solid core by any means known to the art such as bymechanical coating or with an electrically conductive adhesive material.Likewise, the substrate metal may have a hollow core in which a metal ormixture of metals appear such as sodium, potassium or mixtures thereof.These metals may be liquid at the temperature of cell operation to forma completely encapsulated liquid core of excellent electricalconductivity.

By means of the electrode assembly of the instant invention, graphiteanodes no longer need to be handled with assembly jigs and cast in alead base. Furthermore, the production of graphite anodes with taperedends which are designed for wedging into slots or holes is avoided.Likewise, the initial gap between the graphite anodes and the cathodesare accurately set within close tolerances for optimum performance ofthe cell due to the uniform alignment of the electrodes.

Advantages in the electrode assembly of this invention, when employed ina fingered bipolar cell reside in minimized bus bar connections,minimized voltage loss due to bus bar connections and minimizedinvestment for copper used as bus bars.

Additional advantages of bipolar electrolytic cells are that theyrequire less floor space. Consequently, building and piping costs arelower per unit of capacity. The capital investment per unit ofproduction should be less for bipolar cells than for monopolar cells. Anumber of bipolar cells may be contained in one box. Therefore, the cellcontainers may cost less than those presently used for monopolar cellseven though the materials for their construction are more expensive.Rectifier costs are lower for a number of moderately sized bipolar cellsthan for high current rated cells. The cost per kilowatt ofrectification is higher for low voltages and high amperages than forhigher voltages and moderate amperages.

The invention is best understood in all its ramifications by consideringthe drawings.

FIG. 1 is a top view of the fingered bipolar cell of this invention withthe top of the cell removed. A partial section is shown to illustratethe assembly of the electrodes.

FIG. 2, is a side section of FIG. 1.

FIG. 3, is a side section of FIG. 1 taken along view 3-3.

FIG. 4 is a magnified view of the anode-cathode assembly at the top andbottom of the cell, with the cell liquor outlet.

FIGS. 5 and 6 are magnified top views of the anode connection of thebacker plate employing platinum-titanium and graphite electrodes,respectively.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIGS. 1 and 2 theelectrolytic cell series depicted illustrated the use of graphite anodes10 of this invention. The spacer bars 11 are attached to the base plates12. The pressure bars 13 clamp the graphite anodes 10 perpendicularly tothe base plate. Sealant 14 completely seals the spacer bars and pressurebars to form a substantially impervious seal against attack from theanolyte liquor. The cathode fingers 15 project between the anodes. Theends of the base plates 12 are coated with a rubber or plastic lining 16where they extend to the cell casing 17. The base plates 12 aresupported by support bracket which serves as a guide for the base plateduring assembly. Conductors 28 serve to complete the electrical circuitto the cathode screen 15 and as cathode support ribs to prevent collapseof the cathode screen onto base plate 12. Cell liquor outlets 19 areprovided for liquid removal. Outlets 18 are provided for removal of thehydrogen gas product of the electrolysis.

The cell casing 17 may be constructed with steel or plastic. The liner16 for cell casing 17 is coextensive with all exposed internal parts ofthe casing 17. The liner 16 may be rubber or a plastic material such asafter chlorinated polyvinyl chloride with a chlorine content by weightwithin the range of from about to about 76 percent. Other acceptableresins such as chlorinated polyesters may be employed. It is desirableto use resins which are highly filled with sand, SiO graphite particlesor other inert materials as the cell liner.

The base plates at each end of the cell are rubber or plastic linedindependently from the box so that they may be removed readily forrebuilding. A gas-liquid tight junction may be formed between the endbase plates and the cell box by any suitable means such as bolting insuch manner as to form a sealed joint.

In FIG. 3, the arrangement of the anodes 10 upon the steel back plate 12is shown. The bolts 21 extend through the anodes 10 and the slottedholes in the spacer bar 11. Conductors 28 have circulation channelsinterconnecting the cathode compartments to aid in the flow of catholytefrom chamber to chamber. The location of outlet 19 for withdrawal ofcell liquors is shown in relationship to the base plate 12 and supportbracket 30. A hydrogen outlet (not shown) is similarly constructed witha duct running upward to a point above the cell liquor level. Chlorinerises in the cell liquor to a common chlorine space above theelectrolyte from which it flows to a header for ultimate collection.FIGS. 1 and 3 show only one bi-polar unit but any reasonable number ofsuch unit may be included in a box.

FIG. 4 presents the arrangement of the back plate 12 and its assemblageat the top and bottom. The spacer bar 11 contains slotted holes 20through which bolts 21 pass to connect the anode 10 to the backplate. Anasbestos rope, liner or other functionally equivalent means may beplaced in the slotted hole 20 over the bolt 21 to separate the bolt fromsealant 14 to make the task of disassembly easier. The entire exposedsurface of back plate 12 and spacer bar 11 is protected from the cellliquors and products by plastic sealant 14 while rubber or plastic liner16 protects the base plate where it meets the side or bottom of thetank. The cathode support ribs 28 with catholyte flow spaces 34 areconnected to the base plate 12 by welding or by any method that willinsure adequate strength, electrical conductivity and corrosionresistance toward cathodic activity. The cell liquor outlet 19 and thehydrogen outlet 18 pass through the cell casing 17 at the bottom of thecell. The opening through cell casing 17 is lined with rubber or plastic16 and a gasket 32 is inserted between the cell liquor withdrawal meanswhere they join. The gasket 32 may be made of gum or soft rubber orother suitable material. FIGS. and 6 present the electrode assembly ofthe instant invention in conjunction with the use of metal electrodes 23and graphite anodes 10, respectively. The spacing bar 11 is attached tothe steel base plate 12 by Welding, brazing, tinning, bolting or by anymethod EXAMPLE I The following results were obtained during theelectrolysis of feed brine containing NaCl in the stated concentrationwith graphite anodes cast in lead and covered with mastic as isconventional in the art.

TABLE I.GRAPHITE ANODEELECTRICAL CONNECTION CAST IN LEAD 0.9 AMPERE PERSQUARE INCH Feed brine Anolyte Percent Catholyte, g.p.l. Anode gascurrent NaOl, NaCl, Temp. Cell effig.p.l. pH g.p.l. pH NaCl NaOH 0.voltage 0 O 0 2 C O ciency EXAMPLE II which will assure adequatestrength and electrical conductivity. The bolt 21 is passed through thepressure bar 13, the anodes, the spacing bar 11 and tightened on thepressure bar 13. The pressure bars may be transported as may the bolt inthe assembly. The downflow space 24, the interelectrode space 27 and thecathode compartment TABLE IL-GRAPHITE ANODE-ELECTRICAL CONNECTION BOLTEDTO BLADE 0.9

AMPERE PER SQUARE INCH Feed brine Anolyte Percent Catholyte, g.p.l.Anode gas current NaOl, NaCl, Temp. Cell efttg.p.l. pH g.p.l. pH NaClNaOH 0. voltage 002 0 CO ciency.

NOTE: Initial feed brine contained 3.8 percent NazSOr. Approximately 0.5percent CO comes from feed brine 26 form the cell compartments. Theplastic sealant 14 covers the attachment assembly for the electrodes andrubber or plastic 16 lines the base plate Where it meets the side of thetank.

To illustrate the application of the anode assembly of this inventionwith clamped anodes, a comparison of operating conditions of an actualelectrolysis is presented in the following examples. The concentrationof various EXAMPLES III AND IV The following examples illustrate theoperation of an electrolytic cell with platinized-titanium anodes (TypeB-Englehard Coating) bolted directly to the copper bus as described inthis specification. Highly filled polyester resin, described supra, wasused to insulate the anode connection from the anolyte.

TABLE III.PLAT1NIZED TITANI UM ANODE 0.9 AMPE RE PE It SQUARE INCH Feedbrin o Auolyte Percent Catliolyte, g.p.l. Anode gas current NaCl, NaCl,Temp. Coll ellig.p.l. pH g.p.l. pH NaCl NaOH C. voltage 02 CO ciencyNOTE: Initial feed brine contains 3.8 percent N 112803. Source of CO2comes from iced brine.

TABLE IV.-PLATINIZED TITANIUM ANODE 0.9 AMPERE PER SQUARE INCH Feedbrine Anolyte Percent Catholyte, g.p.l. Anode gas current NaCl, NaOl,Temp. Cell effig.p.l. pH g.p.l. p11 NaCl NaOH 0. Voltage CO2 02 COciency Electrolytic cells equipped with the anode assemblies of thisinvention may be operated at considerably higher current densities thancells now operating. The anode assembly of this invention may be used inthe operation of diaphragm type chlorate cells, chlor-alkali cells,monopolar cells and bipolar cells.

EXAMPLE V A laboratory size (50 amperes) monopolar type electrolyticcell equipped with a platiniZed-titaniurn anode bolted to the bus barwas employed in the electrolysis of sodium chloride brine containing upto 3.8 percent sodium sulfate. An asbestos diaphragm was employed andthe cell temperature was maintained at 94:t2" C. The current densitiesas high as about 260 amperes per square foot were achieved withoutencountering excessive voltage. The data presented in Table V was takennear the end of the experiments at which time the condition of thediaphragm and depletion of the electrolyte in the cell exaggerated thecell voltage readings and current efiiciency.

TABLE V.EXIERI1\IENTS IN A LABORATORY SIZE MONO POLAR TYPE CELL ATCURRENT DENSITIES UP TO 260 AMPE RES/SQUARE FOOT Anolytc NaCl PercentCurrent concen- Catllolyte, g.p.l. current density, tration, Cell 6111-G5 arnp./sq.it. g.p.l. pH NaCl NaOH voltage ciencies With clamped anodeassemblies in bipolar electrolytic I cells, higher current densities maybe employed without encountering excessive voltages. This is because theclamped joint between the anode and the current conductor is a lowresistance joint. Likewise, the anode length may be shorter because, byclamping the anodes and sealing them with a plastic sealant as opposedto the conventional mastic or asphalt covering over a poured lead-anodeconnection provides an anode stub loss of about 1 to 2 inches as opposedto a stub loss of 3 to 4 inches.

Normal current densities of between to amperes per square foot may beincreased to as much as 350 amperes per square foot and more with theanode assembly of this invention which provides graphite-copperelectrical connection which is superior to a conventional lead-graphiteconnection.

Having disclosed the invention, it will be apparent that obviousmodifications within the scope of the invention may be made by thoseskilled in the art.

What is claimed is:

1. An electrode assembly for an electrolytic cell comprising a baseplate having a plurality of non-detachable electroconductive spacerbars, two electrodes detachably clamped to each spacer bar and held inposition by two pressure bars and bolt means positioned parallel to saidplate and extending in sequence through holes in a pressure bar, anelectrode, a spacer bar, another electrode and another pressure bar.

2. The electrode assembly of claim 1 in which said electrodes areselected from the group consisting of graphite, a metal, a metal oxideand combinationsthereof.

3. The electrode assembly of claim 1 in which said base plate is steel,said spacer bar is copper and said pressure bars are steel.

4. The electrode assembly of claim 1 in which the spacer bar, electrode,pressure bar and base plate connections are sealed from attack by theelectrolysis prodnets of an electrolytic process by a plastic sealant.

5. An electrolytic cell comprising container means; means for supplyingan electric current to the electrodes; and means for introducingreactant and removing products, said electrodes comprising anodes andcathodes separated by a diaphragm, said cathodes defining plural pocketswhich extend into the spaces between the anodes, said anodes extendingfrom a base plate having a plurality of non-detachable electroconductivespacer bars, said anodes being clamped to said spacer bars by bolt meansdisposed parallel to the base plate, said bolt means extending insequence through holes in a pressure bar, an electrode, a spacer bar,another electrode, and another pressure bar.

6. The electrolytic cell of claim 5 in which said means for supplying anelectric current to the electrodes comprises a monopolar base plate atone end of the cell, said monopolar base plate being separated andinsulated from the cell box by liner means and being connected to asource of electricity.

7. The electrode assembly of claim 5 in which said electrodes areselected from the group consisting of graphite, a metal, a metal oxideand combinations thereof.

8. A diaphragm type electrolytic cell of the fingered bipolar typecomprising a plurality of anodes extending from a base plate and aplurality of cathode pockets extending from a juxtaposed base plate tothe spaces be- III tween the anodes, means for introducing reactant andremoving products, means for supplying electrical energy to saidelectrodes, said base plate having a plurality of non-detachableelectroconductive spacer bars, said anodes being clamped to said spacerbars by bolt means disposed parallel to the base plate, said bolt meansrunning in sequence through a pressure bar, an anode, a spacer bar,another anode and another pressure bar.

9. The electrode assembly of claim 8 in which said electrodes areselected from the group consisting of grahpite, a metal, a metal oxideand combinations thereof.

References Cited UNITED STATES PATENTS 776,490 12/1904 Briggs 2042861,815,080 7/1931 Smith 204-254 TA-HSUN G TUNG, Primary Examiner US. Cl.X.R.

22 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent NO-3,563,878 Dated February 16 197] Inventor(s) Mocri s P Grotheer It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column line 20, change "il lustrated" to read i l lustrates Column 5,line 4 change transpor ted" to read transposed Column 6, Example II,Table 11, under "Percent Current Efficiency" change "8.63" to 86.3

Columns 7 and 8, Table III Footnote, change "Na S0 to Na S0q Column 8,line 59, Claim 1, change said plate" to said base plat Column 8, line7], Claim l, change "by the electrolysis" to ---by the electrolyte andelectrolysis Column 10, line l0, change "grahpi te" to graphite Signedand sealed this 2nd day of November 1 971 (SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer ActingCommissionerof Patent:

